This invention relates generally to solid-state electronic wrist watches having an electro-optic time display, and more particularly to a watch incorporating an arm-actuated switch for activating the display of the watch only when the wearer moves his arm in a predetermined manner.
The term "solid-state electronic wrist watch," as used herein, is limited to wrist-borne electronic timepieces provided with an electro-optic time display and having no moving parts. The traditional spring-powered mechanical watch produces rotary motion for driving gearworks that operate the moving hands or time indicators. In those electronic watches which also have a moving hand readout, the oscillations of a balance wheel or the vibrations of a tuning fork are electronically sustained, the oscillations or vibrations being converted into rotary motion for driving the gear train. Hence moving parts are included in electronic watches of this type.
However, in recently introduced types of solid-state electronic watches, electrical pulses derived from a crystal-controlled time base serve to actuate an electro-optic display formed either by light-emitting diodes (LED) or by liquid-crystal elements (LCD). Hence in such solid-state electronic timepieces, no moving parts are entailed.
In a battery-operated electronic watch having moving parts, such as that disclosed in Hetzel U.S. Pat. No. 2,971,323, the time display is continuous, yet the efficiency of the movement is such that the operating life of the small power cell is well over a year. But in a solid-state watch, the power requirements of the electro-optic display, particularly in the case of an LED display, are relatively high; hence should the display be continuous, the life of the battery would be quite brief.
It is for this reason that commercially available types of solid-state watches are provided with a normally quiescent display that is turned on only when the user depresses a push-button demand switch, thereby conserving power and prolonging the life of the battery. In one such watch, the display is programmed so that upon merely touching the push-button switch, the minutes and hours are indicated for an interval of one and one-quarter seconds, whereas continued depression of the switch causes the minutes and hour data to fade and the seconds to appear and to continue to count as long as the button is held in. In this arrangement, precise computation of time is continuous and independent of whether or not it is displayed, so that the moment the switch is depressed, timing signals are applied to the display.
Since the wearer of the solid-state watch has it strapped to the wrist of one arm, he is compelled to use his other arm to reach the switch and activate the time display. This requirement gives rise to certain practical difficulties, particularly if the other arm is engaged in some necessary activity. For example, one who is carrying a package or driving a car cannot press the demand switch on the watch worn on one arm, without first freeing his other arm.
This difficulty is recognized in Kouchi U.S. Pat. No. 3,748,847, which discloses a solid-state watch whose casing is provided at its rear with a rotatable plate operatively coupled to a switch for activating the display. To bring the face of the watch into view, the arm bearing the watch is twisted. This twisting motion causes movement of the skin in contact with the rotatable plate, as a result of which the plate rotates through an angle sufficient to operate the switch associated therewith. A rotatable plate arrangement of this type requires a special and relatively costly watch case, and it complicates the waterproofing of the case.
Alternative approaches to a wrist-actuated switch are found in Bergey U.S. Pat. No. 3,742,699, where in one embodiment the switch is fully enclosed in the case of the solid-state watch and hence requires no special casing structure. However, in this arrangement the switch takes the form of a conductive ball movable within a sleeve, the ball successively completing a circuit between the sleeve and spaced contacts coupled to separate flip-flop circuits to produce an output signal in response to sequential engagement of the contacts by the ball. Hence, in addition to the switch, this arrangement requires a special electronic circuit associated therewith to produce a switching signal.
One serious problem encountered in prior types of arm-actuated switches for solid-state watches is that the switch may be activated by random or accidental arm movements so that a time-display is produced without regard to demand. This inadvertent switching activity results in excessive current drain and shortens the life of the power cell.